Effects of Hyperthyroidism and Hypothyroidism on Rat Growth Hormone Release Induced by Thyrotropin-Releasing Hormone

Abstract

The effect of synthetic thyrotropin-releasing hormone (TRH) on the release of growth hormone (GH) and thyroid stimulating hormone (TSH) was investigated in euthyroid, hypothyroid and hyperthyroid rats under urethane anesthesia. In euthyroid control rats, i.v. injection of TRH (200 ng/100 g body wt) resulted in a significant increase in both plasma GH and TSH. In rats made hypothyroid by treatment with propylthiouracil or by thyroidectomy, basal GH and TSH levels were significantly elevated with exaggerated responses to TRH. Plasma GH and TSH responses to TRH were both significantly inhibited in rats made hyperthyroid by L-thyroxine (T4) treatment. Altered thyroid status may influence GH release and TSH secretion induced by TRH in rats.